Electron gun



United States Patent O 3,004,183 ELECTRON 'GUN Herbert L. Levin, Paterson, NJ., assignor :to International Telephone Aand Telegraph Corporation, Nutley, NJ., a corporation of Maryland Filed-Dec. 3, 1-957., SerrNo. 700,500 12 Claims. (Cl. 313-82) This vinvention relates to electron guns and more particularly to improvements in electrode mounting in electron guns.

Electron discharge devices, such as traveling wave tubes and the like, have electron gun structures which must be accurately positioned within the tube housing with respect to the longitudinal axis thereof.` Further, the electrodes which go to make up the electron gun must be accurately positioned with respect to each other, not only when asspmbled, but when the tribe is in operation. Failure to maintain these accuracies produces faulty operation of :the tube with 4its inherent 'distortion and shortened life.

The problem of supporting electrodes in precise geometric relation within -an electron discharge device is often quite severe. The diiculty arises from the fact that lsuch electrodes must be insulated from cach other 'and yet preferably mounted to insure a fixed spatial relationship therebetween. To achieve geometric precision, it is desirable that the various electrodes mechanically coact together in some fashion, it being virtually impossible to maintain 'a lxed spatial relationship between independently mounted electrodes.

Various schemes have been employed in the past to mount lthe electrodes to foml an electron gun. Each of these 'schemes has had one or more disadvantages. One such scheme employs ceramic spacers between the adjacent transverse surfaces of the electrodes of the electron gun. The outer periphery of the spacers bear against the vacuum housing and the inner surface bears against the outer surface of the electrodes to position the 'electrodes radially. The thickness of the spacers position the electrodes axially. This particular design is expensive and, for some tube sizes, -may be impractical becausethe successful use of the ceramic spacers depends npon concentricity between lan internal diameter and van external diameter and perpendicularity between these diameters and a pair of dat transverse surfaces of the spacers. To obtain all these accurate dimensions on one ceramic spacer requires an internal-external grinding operation which is expensive. Another such scheme employs centerless-.ground ceramic rods bearing against the vacuum housing. The rods have ground therein radial slots to retain the gun elements. The position of the slot along the length of the rods and the depth of the slots must be very accurate. Any slight discrepancies in these dimensions will cause a disaligned electrode structure. Again, the fabrication of this structure is painstaking and relatively expensive.

lIt is an obiect of this invention to provide an improved electron gun structure for electron discharge devices.

Another object of this invention is to provide an improved electron gun structure for electron discharge devices employing electrode positioning members conligured to cooperate in easy outgassiug of the electron discharge device.

Other objects of this invention are to provide an improved support for electron gun electrodes; to provide electron gun electrode supports which are compact, easily fabricated and rugged; to provide electron gun electrode supports which maintain critical alignment and spacing of the gun electrodes relative to each other and to a rectilinear electron beam path; to provide an electron gun Mice electrode vsup'pu'art vvoid of cements and brazing materials for supporting the gun elements; to provide an electron gun electrode support which enables the assembly of an electron gun structure by a stacking process; to reduce the complexity of machining various elements in the electron gun structure; and to provide an electron gun electrode support which will enable the reduction of electron gu'n size.

l A feature of this invention is the provision of means for supporting Ithe electrodes of an electron gun in xed geometric relation comprising the inner surface of the vacuum envelope of an electron discharge device, a plurality of rods of insulating material disposed lengthwise of, in spaced circumferential relation about and bearing against the inner surface of said envelope and a plurality of electrodes each including portions disposed transversely of said envelope to bear against each of said mus to establish the radial alignment of said electrodes. The supporting means in accordance with this invention further includes a plurality of dielectric spacers of generally cylindrical coniiguration disposed to engage each of said rods and intermediate each of said electrode portions to axially space said electrodes thereby establishing a iixed geometric relationship between the electrodes of the electron gun and the longitudinal axis of the electron discharge device.

Another feature of this invention is the provision of a resilient member disposed in coacting relationship with the stem portion of the discharge device and the rods and at least the lirst and last of the dielectric spacers to maintain said electrodes in the established fixed geometric relationship whereby the electrode position is not affected by unequal thermal expansions, vibration, or shock.

Still another 'feature Iof this invention is the provision of slots or depressions in at least one of the transverse surfaces of the ceramic spacer to provide clearance for the electrode voltage lead to electrode connection and further to -serve as :gas ports to facilitate the exhaust operation of the electron discharge device by eliminating .gas ent-rapping pockets in the electron gun structure.

A further feature of this invention is the provision of a ceramic spacer having in its outermost longitudinal :surface longitudinal slots to at least partially encircle the rods t'o lock the rods in a relatively lixed circumferential position about the inner surface 4of the envelope.

Still a `further feature of this invention is the provision of holes parallel to 'the axis of electron gun structure in the ceramic spacers to accommodate the voltage leads from the stem of the discharge device to the various electron gun electrodes and to isolate the leads from each other 'and from other 'than the desired one of the electron gun electrodes.

'The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIG. l is a longitudinal cross-sectional view of the electron gun structure in accordance with the principles of this invention as it would be incorporated in a traveling wave electron discharge device;

FIG. Zis a transverse cross-sectional view taken along lines of FIG. l;

FIG. 3 is a view in perspective of the dielectric spacer employed in the electron gun of FIG. l;

FIG. 4 is a longitudinal cross-sectional view of another electron gun structure employing the principles of this invention;

PIG. 5 is an enlarged view in perspective of a modication of the dielectric spacer of this invention; and

FIG. 6 is a view in perspective of still another modiiication of the dielectric spacer of this invention.

Referring to FIGS. 1 and 2, there is illustrated therein an electron gun 1 following the principles of this invention as it would be employed in connection with a traveling wave type tube. The traveling wave type tube is illustrated as having an interaction section 2 in axial alignment with the axis of electron gun 1. Interaction section 2 comprises a vacuum envelope 3 illustrated to be metallic but which may be composed of dielectric material. Within envelope 3 is disposed the slow wave propagating structure 4 in the form of a helix 5 supported by dielectric support rods 6 and retaining ring 7. Ring 7 is mounted on reference surface 8 of member 9. The elements of electron gun 1, hereinbelow described, are mounted on reference surface 10 of member 9. Also mounted on reference surface 10 is the anode-electrode 11 of the electron gun 1.

Electron gun 1 includes as a major component thereof vacuum envelope 12 depicted in FIGS. 1 and 2 as being composed of metal, but it is to be understood that this envelope may also be composed of a dielectric material, such as ceramic or glass. Other components of electron gun 1 include rods 13 composed of dielectric material, such as ceramic, spacers 14 composed of dielectric material, such as ceramic, and electrodes including cathode 15 and focusing electrode 16, each of the electrodes including a portion disposed transversely of envelope 12 for electrode support and identified as electrode support elements 17 and 18, respectively. Filament 19 is disposed within cathode housing 20 to indirectly heat cathode 15.

Electrode support elements 17 and 18 are necessary in the electron gun 1 of FIG. l to carry out this invention due to the nesting nature of the electrodes thereof. However, it is to be understood that these support elements are a physical and electrical portion of their associated electrodes. While in FIG. 1 there are shown only two electrodes supported in a manner described hereinbelow, more electrodes may be supported in this arrangement by adding spacers and the desired electrodes in accordance with the teachings of this invention.

The improved electron gun electrode support arrangement of this invention separates the functions of the ceramic spacer surfaces of the prior art arrangements and thereby simplifies the machining process of .the spacers. The pair of ilat transverse surfaces 21 and 22 of the ceramic spacers 14 are ground and/or lapped in a manner required to provide the desired reference surfaces for accurate axial parallel spacing of the electrodes 15 and 16 when their respective supporting elements 17 and 18 are disposed between adjacent spacers 14. This is similar to the requirement of the prior art ceramic spacer arrangement. However, in this improved electrode mounting arrangement, there are no concentric diameters required to obtain radial alignment in the ceramic spacers of this invention. Instead, three inexpensive centerless ground dielectric rods 13 are used to obtain radial alignment as follows. A transverse reference surface or ridge 23 is machined in envelope 12 and the inside diameter or surface 24 of envelope 12 is machined accurately if metallic vor formed accurately if glass. The outside diameters of the transverse portion of electrodes 15 and 16, the electrode supporting elements 17 and 18, are machined or stamped accurately and concentrically to their inner diameters. The rods .13 are seated in reference surface 23 and positioned to bear on the inner surface A24 of envelope 12. The electrode support elements 17 and surfaces bear on the rods 13. This will then provide the desired radial alignment. Ceramic rods 13, shown to be three in number, are disposed lengthwise of and circumferentially spaced about envelope 12 substantially as illustrated in FIGS. l and 2. Spacers 14 of proper thickness are disposed between the electrodes to provide the desired axial spacing thereof.

18 are positioned so their outer Spacers 14 are configured to have a hollow cylindrical portion 25 and a hollow ange portion 26 substantially as illustrated in FIGS. l, 2, and 3. Flange portion 26 includes longitudinal slots 27 therein to engage rods 13 and maintain them in a relatively fixed longitudinal, circumferential position about envelope 12. Holes 28 are providedin ange portion 26 for passage of electrode voltage leads 29 from the stem 30 to their respective electrodes. The provision of holes 28 in ange portion 26 serve to insulate and isolate the leads from each other and from other than the desired electrodes. This arrangement improves tube reliability by eliminating internal shorts. The L-shaped cross-section of spacers 14 provide space for the electrode voltage leads to electrode connection as shown at 31 in slots 32 circumferentially spaced about liat surface 21 of spacers 14. The slots 32 provide clearance for the voltage lead connection to the electrode and also serve as gas ports to facilitate the exhaust loperation of the electron discharge device by eliminating entrapped voids in the electron gun.

The individual components of the electron gun structure of this invention lend themselves to assembly by a stacking process. The assembly of an electron gun would be accomplished substantially as follows. Ceramic spacer 14b is positioned to bear against transverse reference surface 23. Rods 13 are positioned lto bear against inner surface 24 of envelope 12 at spaced circumferential points thereabout as determined by slots 27 of spacer 14b and against the transverse reference surface 23. Electrode support element 18 and its associate electrode would be positioned so that the outer longitudinal surface of support element 18 bears against rods 13 while its transverse surface rests on flat surface 21 of ceramic spacer 14h. Ceramic spacer 14a is then positioned to engage rods 13 in slots 27 with its at surface 22 resting against the contiguous transverse surface of support element 18. Electrode support element 17 and its associate cathode would then be positioned so that the outer longitudinal surface of element 17 bears against rods 13 and the contiguous transverse surface of element 17 rests on surface 21 of spacer 14a. Spacer 14 would then be positioned to engage rods 13 in slots 27 and against the contiguous surface of support element 17. This would then provide the desired radial and axial alignment of electron gun electrodes. The axial distances between the various electrodes is determined by any desired spacer thickness. It is also 'possible to have a standard thickness spacer and then employ several spacers between the electrodes to obtain the desired axial spacing.

After the spacers and electrode elements have been assembled in the manner described above, it is necessary to provide an arrangement to maintain the electrodes in their fixed geometric relationship with each other and with the axis of the rectilinear electron beam path regardless of physical shocks, vibrations, or thermal expansion. This is accomplished by spring loading the assembled components. The electron gun assembly is spring loaded by employing spring 33 to bear against surface 21 of spacer 14 and the adjacent ends of rods 13 and stem 30. Spring 33 is placed under axial compression when stem'30 is secured to the inner surface 24 of envelope 12 by means of welding or brazing.

FIG. l illustrates the radial and axial alignment of nested electrodes following the principles of this invention. The teachings of the invention are not limited to this type of electrode. The teachings of this invention may be applied to various electrode configurations, one of which is the common disc-type electrode. FIG. 4 illustrates how the teachings of this invention would be utilized to support a plurality of disc-type electrodes in radial andlaxiall-alignment to form an electron gun. While spacer 14 of FIG. 1 could be employed in the embodiment of FIG. 4, -a modification of spacer 14 is illustrated in FIGS. 4 and 5 to illustrate some of the many variations of this invention. It is :to be understood, however, that the spacers depicted :in FIGS. l and 4 and variations such as illustrated in FIG. 6 are not limited to use with a particular electrode configuration; they are interchangeable.

Referring in greater particularity to FIGS. 4 and 5, electrodes 34 are supported radially as described in connection with FIG. 1 by the accurately dimensioned inner surface 35 of envelope 36, the accurately dimensioned rods 37 and the accurately dimensioned and concentric inner and outer diameters of electrodes 34. Thus, rods 37 are disposed against surface 35 of envelope 36 and electrodes 34 are disposed so that their outer surface bears against rods 3.7. The axial spacing of electrodes 34 is provided by dielectric spacers 318. These spacers 38 have the same function as spacers 14 of FIG.Y '1 but have a slightly different configuration which are easier to manufacture. yThe spacers 38 are hollow cylinders .with a substantially .uniform outside diameter containing slots 39 to engage rods 37 for positioningthereof. At least one transverse surface, such 'as surface 40, includes therein a depression 41 which facilitates the connection of the voltage leads to the contiguous electrode, such as at 42 in FIG. 4, with the voltage leads being brought to this electrode through holes v43 disposed within ydepression 41.

It is to be remembered that electrodes 34 have a transverse portion bearing against rods 37 to establish radial alignment thereof and thus is equivalent to the electrode supports of electrodes .and 16 of FIG. 1. Thus, when the phrase an electrode having portions disposed transversely of the envelope is employed in the claims, it is considered that the phrase will read on the electrode coniiguration of FIGS. l and 4 .and other electrode configurations having the desired transverse portions.

FIG. 6 shows still another modification of spacers 14 of FIG. 3 and spacer 38 of FIG. 5. The modification of FIG. 6 is configured to be a cylinder 44 having slots 45 in one transverse surface thereof. This spacer does not include a iiange portion as does spacer 14 of FIG. 3, nor

does it include the longitudinal slots of spacers 14 and 38 of FIGS. 3 and 5. The outer surface of cylinder 44 is positioned to merely bear against rods 13 since the longitudinal slots in the outermost surface are not present. This spacer is of course cheaper to manufacture than the previous two modifications. Since the longitudinal slots are not present, the spacer cannot hold the rods in their circumferential spaced relation. Thus, it is necessary to provide at the ends of the rods metal clamps to retain the rods in their fixed circumferentially spaced position. Also, when this type of spacer is employed, it is necessary to provide separate insulation for the voltage leads to the various electrodes of the electron gun since no longitudinal apertures are provided in the dielectric spacers.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

l. In a vacuum tube having a plurality of electrodes, means for supporting the electrodes in fixed geometric relationship comprising a cylindrical vacuum envelope, the inner surface of said envelope providing the primary reference surface for said supporting means, a plurality of cylindrical rods of insulating material disposed lengthwise of and in spaced circumferential relation about said inner surface, said rods each including a first surface portion along the length thereof bearing against said primary reference surface in substantially a line contact and a second surface portion along the length thereof opposite said rst surface portion cooperating to provide a secondary reference surface for said supporting meansspaced radially from and concentric to said primary reference sur- 6 face, a plurality rofV electrodes each `including a portion 'disposed .in transverse relation to `said envelope, each of said transverse portions being a relatively thin, `annular member .having paralleltransverse surfaces and inner and outer ycircumferences concentric with respect to each other and perpendicular to said transverse surfaces, the outer vcircumference of said annular member of each of v'said transverse portions bearing against said'second surface portion of each of said rods to establish the radial alignment of said electrodes, a plurality of hollow .dielectric spacers of generally cylindrical configuration .having the end surfaces thereof parallel with respect to each other, veach of said spacersbeing disposed to engage said second surface portion fof each 'of said rods by at least a portion of the outer surface thereof and to have the end portions thereof in contact with the juxtaposed transverse surfaces of said annular members of adjacent ones of said electrodes to axially space said electrodes within said envelope and to dispose each of said annular members in a parallel relationship with respect to each other to render the inner circumference of each of said annular members concentric with respect to said primary and secondary reference surfaces, and means disposed in coacting relation with the ends yof said rods and the end surfaces of at least the first and last of said spacers to maintain said annular members bearing aganst'said second surface portion of said rodsand `in contact with said spacers and to maintain lsaid first surface portion of said rods bearing against said primary reference surface to retain said electrodes in the established fixed geometric relationship.

2. A vacuum tube according to claim l, wherein each of said spacers includes longitudinal slots in the outer most extremity thereof to engage said rods.

3. A vacuum tube according to claim l, wherein each of said spacers includes an outwardly extending flanged portion havingr longitudinal slots in the outer lsurface thereof to engage said rods.

4. A vacuum tube according to claim 1, wherein at least one of the end surfaces of each of said spacers includes a plurality of circumferentially spaced depressions therein to provide gas ports.

5. A vacuum tube according to claim l, wherein said means to maintain said electrodes in the established fixed geometric relationship includes ya resilient member.

6. A vacuum tube according to claim 1, further including voltage leads lfor said electrodes and said spacers include longitudinal apertures therein for passage of said leads. f

7. A vacuum tube according to claim 6, wherein each of said spacers includes at least one depression on at least one transverse surface thereof contiguous to the adjacent one of said electrodes and the appropriate one of said leads is connected to said adjacent one of said electrodes in said depression.

8. An elect-ron gun structure comprising a cylindrical vacuu-m envelope, the inner surface of said envelope including a first portion having a first given diameter providing a first reference surface, a second portion adjacent one end of said envelope having a second given diameter less than said vfirst diameter and a circular rid-ge disposed to interconnect said first and second portions Ito provide a second reference surface perpendicular to said iirst reference surface, a plurality of cylindrical rods of insulating material disposed to have one end thereof seat on said second reference surface, said rods each including a first surface portion along the length thereof bearing against said first reference surface in substantially a line contact and a second sunface portion along the length thereof opposite said first surface portion cooperating to provide a third reference surface spaced radially from and concentric to said first reference surface, a plurality of electrodes each including a portion disposed in transverse relation to said envelope, each of said transverse portions being a lrelatively thin, annular member having parallel transversesurfaces and inner and outer circumferences concentric with respect to each other and perpendicular to said transverse surfaces, the outer circumference of said annular member of each of said transverse portions bearing `against said second surface portion of each of said rods to establish the radial alignment of said electrodes, a plurality of hollow dielectric spacers of generally cylindrical configuration having the end surfaces thereof parallelwith respect to each other, each of said spacers being disposed to eng-age yby at least a portion of the outer surface thereof said second surface portion of each of said rods and to have the end portions thereof in contact with the juxtaposed transverse surfaces of said annular members of adjacent ones of said electrodes to axially space said electrodes within said envelope and to dispose each of said annular members in a parallel relationship with respect to each other to render the inner circumference of each of said annular members concentric with respect to said first and third reference surfaces, a stern portion having voltage leads therein for connection to said annular member of appropriate ones of said electrodes disposed to close said envelope adjacent the end thereof removed from said second reference surface, and resilient -means disposed in coacting relation with that portion of said stem portion within said envelope, the ends of said rods `adjacent said stem` portion and the end surface of sa-id spacer adjacent said stem portion to maintain said annular members bearing against said second surface portion of said rods and in contact with said spacers and to maintain said rst surface portion of said rods bearing against said first reference surface and the ends of said rods bearing against said second reference surface to retain said electrodes in the established tixed geometric relationship.

9. A structure according to claim 8, wherein each of said spacers includes a hollow cylinder having longitudinal slots in the outerl surface thereofcircumferentially spaced to engage said rods. f

l0. A structure yaccording to claim 9, wherein each of said spacers includes a depression in one transverse -surface thereof and a plurality of apertures extending longitudinally through said spacers in the region of said depression for passage of said voltage leads and the appropriate voltage lead is coupled to the electrode contiguous said one transverse surface in said depression.

ll. A structure according to claim 8, wherein each of said spacers includes a hollow cylinder having an out- -wardly extending ilange on one end thereof, said tiangc having longitudinal slots in the outer surface thereof circumferentially spaced to engage said rods.

12. A structure according to claim 11, wherein each of said spacers includes a plurality of slots in the transverse surface of the cylinder portions and a plurality of apertures extending longitudinally through the flange portions for passage of said voltage leads and the appropriate voltage lead is coupled to the electrode contiguous the transverse surface of the cylinder portion in one of said slots.

Coulson Mar. 5, 

